In the first trimester, which adnexal mass is most commonly observed and associated with progesterone production?

• A. Corpus luteum
• B. Ovarian cystadenoma
• C. Dermoid
• D. Theca lutein cyst

Answer: (A)

The main idea is how the corpus luteum functions in early pregnancy. After ovulation, the ruptured follicle becomes the corpus luteum, and this structure secretes progesterone to prepare and maintain the uterine lining for implantation. If pregnancy continues, the placenta eventually takes over progesterone production, but during the first trimester the corpus luteum is the primary source of this hormone. On ultrasound, it often appears as a cystic structure within the ovary and may contain hemorrhagic content; Doppler typically shows peripheral vascularity around the wall.

This makes it the most common adnexal mass seen in early pregnancy and the one specifically associated with progesterone production. Other masses, like theca lutein cysts, dermoids, or cystadenomas, can occur but are not the typical progesterone-producing mass seen in the first trimester.